BASALTBasalt is the most abundant extrusive rock. Basalt forms the Earth's crust, including the oceanic crust, shield volcanoes, and lava plateaus.

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GRANITEGranite is the most abundant intrusive rock. Granite forms the core of many mountain ranges.
Granite used in a number of monuments and gravestones. The strength of granite allows it to stand up against natural weather conditions, allowing for a long lifespan. Its beauty also contributes to the intended striking impression of monuments. Granite is also commonly used for kitchen countertops.

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TEXTURETexture of the rock depends on the size and shape of its mineral crystals.

Igneous rocks may be:

coarse-grained
fine-grained
glassy
porphyritic

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PORPHYRITIC TEXTUREThis is an igenous rock texture in which large crystals are scattered on a background of much smaller crystals. Porphyritic rocks form when crystals cool in two stages.

EXTRUSIVE ROCKS
FINE-GRAINED - formed from rapid cooling lava (small crystals)
GLASSY - composed of crystals too small to see

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MINERAL COMPOSITIONThe silica content of magma and lava affects how easity the magma or lava will flow.

Lava that is low in silica usually forms dark-colored rocks such as basalt.
Magma that is high in silica usually forms light-colored rocks, such as granite.

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Uses of Igneous RockIgneous rock is hard, dense, and durable. For this reason people throughout history have used igneous rocks for tools and building materials.
Granite was used by Ancient Egyptians for statues.
Basalt is crushed to make gravel that is used in construction.
Pumice is used for cleaning and polishing.